Test failure with --features=desktop-notifications

[osa1]

Originally reported in https://github.com/NixOS/nixpkgs/pull/243860/files#r1266384829.

$ cargo test --features=desktop-notifications
...
---- tests::config::parsing_tab_configs stdout ----
thread 'tests::config::parsing_tab_configs' panicked at 'assertion failed: `(left == right)`
  left: `Some(TabConfig { ignore: Some(true), notify: Some(Off) })`,
 right: `Some(TabConfig { ignore: Some(true), notify: Some(Mentions) })`', crates/libtiny_tui/src/tests/config.rs:70:5
stack backtrace:
   0: rust_begin_unwind
             at /rustc/90c541806f23a127002de5b4038be731ba1458ca/library/std/src/panicking.rs:578:5
   1: core::panicking::panic_fmt
             at /rustc/90c541806f23a127002de5b4038be731ba1458ca/library/core/src/panicking.rs:67:14
   2: core::panicking::assert_failed_inner
   3: core::panicking::assert_failed
             at /rustc/90c541806f23a127002de5b4038be731ba1458ca/library/core/src/panicking.rs:228:5
   4: libtiny_tui::tests::config::parsing_tab_configs
             at ./src/tests/config.rs:70:5
   5: libtiny_tui::tests::config::parsing_tab_configs::{{closure}}
             at ./src/tests/config.rs:7:26
   6: core::ops::function::FnOnce::call_once
             at /rustc/90c541806f23a127002de5b4038be731ba1458ca/library/core/src/ops/function.rs:250:5
   7: core::ops::function::FnOnce::call_once
             at /rustc/90c541806f23a127002de5b4038be731ba1458ca/library/core/src/ops/function.rs:250:5
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

We should start running tests with desktop-notifications. The other feature we have is about TLS, which we don't test, so there will be just one more test configuration.